Signal transduction via protein phosphorylation is a major mechanism whereby extracellular stimuli regulate intracellular functions. Protein phosphorylation is of particular importance in the brain: neurons are the body's richest cellular source of protein kinases (protein phosphorylating enzymes) and their substrate proteins. Changes in the phosphorylation state of these substrate proteins typically result in a profound effect on the biology's of those substrate proteins. Alzheimer's disease is the major cause of primary brain failure and is characterized by neurochemical deficits and the accumulation of intraneuronal and extracellular pathological structures. In the Alzheimer brain, there are likely to be important interactions between the structural-neurochemical pathology and the systems of signal transduction via protein phosphorylation. The overall goal of this application is to define and characterize those interactions, with an emphasis on identifying pathways with potential for therapeutic intervention. Specifically, we propose a multidisciplinary approach, from several perspectives. We propose to study the effects of protein phosphorylation on the expression, catabolism, and intracellular trafficking of the Alzheimer amyloid precursor protein (APP), the primary biochemical component of parenchymal and perivascular amyloid deposits. In order to provide independent and parallel evidence for the significance of effects of phosphorylation on APP metabolism, a highly related protein from a divergent species (the APP-like protein from Drosophila) will also be studied. A comprehensive study of the role of protein phosphorylation in APP expression will also be undertaken, with particular emphasis on the APP promoter-binding homeoproteins, several of which are known to be phosphoproteins. A broad and systematic regional survey of protein phosphorylation systems will be performed in rapidly processed human brain, including normal young, normal aged, and Alzheimer tissue. Enzymological, immunochemical, immunocytochemical and molecular biological approaches will be used. A multidisciplinary effort will also be made to determine whether APP, like many other transmembrane proteins, can function to transduce signals across the plasmalemma. Chimeric molecules, joining APP domains with counterparts from characterized transducing proteins, will be expressed in cells, forming the basis for assays of signalling capability. In summary, the experiments proposed in this application are designed to identify interactions of Alzheimer-related neuropathology with the vital neuronal system of signal transduction via protein phosphorylation. We place particular emphasis on identifying potential target pathways by which protein phosphorylation would either regulate the production of Alzheimer- type pathology, or alternatively, pathways of protein phosphorylation which might be aberrant as a result of the disease and whose therapeutic correction might ameliorate the cognitive failure of Alzheimer's disease.